Heating system



NQV- 30 W HEATING SYSTEM Filed March 1, 1946 2 Sheets-Sheet 1 m C) r 77k 66 76 u 75 75/ 74 j i INVENTOR. 2 mm 11/ MCI/11m),

m w/M Nov. 30, 148- w. W. HALLINAN HEATING SYSTEM 2 Sheets-Sheet 2 FiledMarch 1, 1946 \A l J INVENTOR.

wA/WM W M W Patented Nov. 30, 1948 UNITED STATES PATENT-OFFICE HEATINGSYSTEM William W. Hallinan, Racine, Wis.

Application March 1, 1946, Serial No. 651,177

Claims. (01. 237-2) The present invention relates to heating systerns,and is particularly concerned with heating systems of the type employinga warm air furnace or other source of heated air. In-the warm airfurnace installations of the prior art the size of the furnace, thenumber, and size of hot or cold air ducts are proportioned with respectto the size and character of the rooms that are to be heated and theirlocation, number of windows, etc. Thus, when the installation iscompleted, the size of the ducts is so proportioned that when all of theregisters are open, the system is balanced and each room will receiveits predetermined amount of warm air, which is calculated to keep therooms all at the desired temperature.

Although such systems are balanced when all of the registers are open,they are not balanced when any registers are closed; and this isparticularly bad, as the blower is adapted to provide the volume of hotair which is necessary for all of the rooms, and this conditioncontinues even though the user has closed a number of registers.

The housewife may, and does, often close off the registers leading tothe sleeping rooms or to parlors or other rooms which are not usedfrequently or which she may desire to keep cool.

This causes a large volume of hot air, which was intended to heat therooms that have been shut off, to be poured out into the remainingrooms, giving a condition of high, uncomfortable air velocity andoverheating.

One of the objects of the present invention is the provision of animproved heating system wherein the closing of any of the registers atthe hot air output into the rooms will regulate the conditions existingat the furnace so that the volume of air passing through the bonnet ofthe furnace is constantly proportioned-to the number of registers whichmay be open, thus keeping the system in a balanced condition at alltimes.

Another object of the invention is the provision of an improved heatingsystem in which the volume of air passing through the furnace bonnet isconstantly proportioned to the number of registers which may be open atany time and in which the opening of a register correspondinglyincreases the volumeof air passing through the furnace bonnet so as tosupply that register with its proper amount of air, while stillsupplying all of the others.

Another object of the invention is the provision of an improved systemwherein the closing of any register is adapted to bring about a chain ofevents which results in the reduction of the volume of the air passingthrough the furnace 2 bonnet by an amount which is substantially equalto that which would be required by the register or registers which areclosed.

\ Another object of the invention is the provision of a modified,improved system in which the volume of air that is driven through afurnace bonnet by means of a blower is constantly proportioned to thetemperature of the air which is being supplied by the furnace. D Anotherobject of the invention is the provision of an improved heating systemin which the blower is adapted to be driven by a thermostaticallycontrolled variable diameter pulley on the shaft of a constant speedmotor and in which the volume of air supplied to the furnace bonnet isproportioned to the number of registers that is open at any time.

Another object of the invention is the provision of improved heatcontrol devices of the class described which are simple, capable ofbeing installed in the existing heating systems, and adapted to be usedfor a long period of time without necessity for repair or replacement.

Another object of the invention is the provision of an improved heatingsystem in which the volume of air delivered through the registers iscontrolled by both its temperature and its pressure.

Other objects and advantages of the invention will be apparent from thefollowing description and the accompanying drawings, in which similarcharacters of reference indicate similar parts throughout the severalviews.

Referring to the drawings, of which there are two sheets, Fig. 1 is adiagrammatic elevational view of a heating system embodying the presentinvention;

Fig. 2 is a fragmentary elevational view, with a hot air pipe insection, showing the application of the mechanism of this systeminstalled in the partition of a standard winter air conditioning unit,with the two dampers mounted upon a single shaft;

Fig. 3 is a fragmentary sectional side elevational view of the mechanismof Fig. 2;

Fig. 4 is a similar view to Fig. 1 of a modification in which thedamper, which regulates the volume of cold air, is regulated by thetemperature of the air in the bonnet or being discharged from the hotair ducts of the bonnet;

Fig. 5 is a diagrammatic'elevational view of another modified heatingsystem, in which the speed of drive of a blower is regulatedproportionately to the number of registers that may be open by varyingthe amount of hot air delivered I the bracket 83. In other embodimentsthe end of a hot air furnace including any suitable source ofheat, suchas gas, oil, or coal burner, and this bonnet is provided with aplurality of hot air discharge conduits l I, I2 at the top and with acold air inlet i3 at the bottom.

The cold air inlet connects with a housing i l of a centrifugal blowerl5, which has its intake located at either or both ends of the shaft IS.The centrifugal blower I5 is located in a cold air duct or housing H,which communicates with a cold air inlet duct l8 and may be providedwith the usual air filter i9. The centrifugal blower I5 has the usualcentrifugal impeller on the shaft l6, which isdriven by'a V pulley 20 ofthe type shown in Fig. 7. The pulley 20 is driven by means of V belt 2|,which also engages the V drive pulley 22 on the shaft 23 of a constantspeed motor 24. i 1

The present blower system is preferably provided with a damper 40located in the inlet to the furnace bonnet ill that is the outlet fromthe blower housing M.

In other embodiments of the invention the damper 40 may be located inthe inlet to the housing I or the hot air ducts ii, l2, or the inletconduit i8 to the cold air duct i'l. This damper 40 is adapted to effecta control of the volume of air being driven through the furnace bonnet Iresponsive to the action of a thermostat 4l. This thermostat may consistof a closed metallic bellows filled with a suitable supply ofrefrigerant, such as Freon, one end of the bellows being secured to theupper arm 42 of a supporting frame 43.

The lower end of the bellows may be carried by the circular plate 44 ofa plunger 45 that is slidably mounted in a bore in the lower arm 46 ofthe frame 83.

The plunger 45 is pivotally connected at 4? to a link 48, which ispivotally connected at 49 to a lever 50. The lever 56 has one endpivoted at i to a bracket carried by the wall of the furnace casing 9and the other end is pivotally connected at 52 to a link 53, which ispivotally connected to the bellcrank arm 54 at 55.

The bellcrank arm 54 is fixedly secured to the damper 40. The damper 40is preferably arranged in such a position that it is closed or almostclosed when the thermostat M is cold; but, when the thermostat 4i isheated, it moves the plunger 45 downward, acting on the lever 56 andlink 53, moving the damper 40 in a clockwise direction in Fig; 1 toeffect an opening of the inlet i3.

' The thermostat 4i may be subjected to the temperature of airdischarged from the furnace bonnet ill by having another conduit 56extending from the top of the furnace bonnet down into the cold air ductH.

In this case the end of the conduit 56 partially surrounds thethermostat 4!, which may be accomplished by merely beveling off the endof the conduit 56 so that the end does not interfere with Iii of theconduit 56 may be slotted for the bracket arm 42 and extended tosurround the bellows 4i so as to bring the warm air into closer contactwith the thermostat 4!.

Thus, the contraction of the bellows 4| tends to maintain the cold airinlet i3 closed except when the furnace is heated and hot air dischargedfrom the furnace bonnet i0 is of such temperature asto cause expansionof the thermostat ii, tending to open the inlet i3.

The hot air ducts 'II and I! are each provided with a suitable register51, 58, preferably of the type having a plurality of louvers 59 joinedby an actuating bar 60, which can be actuated by means of a hand lever6| to open or close the louvers. Any type of register, however, may beemployed which is provided with a closure, such as an automatictemperature-controlled register operated by a room thermostat.

One of the hot air ducts, such as the airduct l 2, is preferablyprovided with a pressure responsive device of the type indicated at 62.This consists of a laterally extending housing 63, which is providedwith an end wall 64 that is curved to fit the pipe or conduit I 2 at itsupper edge, two side walls 65, and an end wall 66.

Like the end wall 64, the upper edge of the end wall 66 is curved to fitthe pipe i 2, but the end wall 66 is formed to be partially cylindricalupon a center which corresponds to the center of pivot 61 of a pressurevane 68.

The pressure vane 68 is pivoted at 61 upon the lower edge of the wall 64and is provided with a rearwardly extending balance arm 69, carrying anadjustable weight Ill. The housing 65 is preferably rectangular inbottom plan, and the vane I 68 in complementary in shape, that is,rectangular, so that its edges are only slightly spaced from the sidewalls 65 and from the cylindrically curved end wall 66.

Thus, the vane 68 may move pivotally with a I minimum amount of frictionand a minimum amount of air leakage. It may be actuated by very slightchanges in pressure in the entire system, which includes the furnacebonnet l0 and air ducts ii, l2. The pivot shaft 61 for the vane 68preferably has a laterally extending crank arm ll, which is pivotallyconnected at 12 to a link 13 that is pivotally connected at 1'4 to adamper arm 15.

The damper arm 75 is fixedly secured to a I damper shaft 16, whichcarries a butterfly damper 11 located in the hot air pipe. 56 thatconducts the hot air to the thermostat iii. The operation of this formof mechanism is as follows:

When the heating system is installed, the sizes of the furnace bonnetand the various conduits are made such that each room gets the desiredamount of heat when all of the registers are open. Were it not for themechanism of the present invention, when one or more of the registers isclosed, the system would be out of balance; and the hot air, which wouldotherwise go to the room where the register is now closed, would beconducted to other rooms, with the result that. although one register isclosed, a larger amount of hot air pours out of the other hot air ducts,creating high air velocities and overheating' the other rooms.

When one of the registers is closed, this naturally causes an increasein the static pressure in the various ducts of the heating system. Suchan increase of pressure may amount to only a few ounces or a fraction ofan ounce, but the vane 88 is quite sensitively balanced by means of anadjustable weight 10.

According to my invention, any increase in the static pressure in theconduit l2 causes the vane 68 to be moved downward from the full lineposition to the dotted line position or to some intermediate position,

As the vane 68 moves downward, the crank arms and links H, 15, 13 tendto turn the butterfiy damper 11 so as to throttle the amount of hot airthat is fed to the thermostat 4|. Ordinarily the butterfly damper isclosed when the furnace is cold and opened as the furnace comes up toproper heat, so that the heating of the thermostat 4| tends to open thedamper 4|].

An throttling of the heated air in the conduit 56 diminishes the hot airthat pours upon the thermostat 4 and this hot air, being mixed with coldair in the housing 11, the heating effect on the thermostat 4| isdiminished. Thus, whenever, a register is closed, the vane 68 isactuated to a predetermined degree, closing the damper 11 to apredetermined degree, diminishing the heat on the thermostat Al andtending to close the damper 40 to a predetermined degree.

Closing of a register thus diminishes the amount of air which is driventhrough the heating system by the blower. Closing of two registers willdiminish this amount of air still more and causes the damper 40 to closestill further, diminishing the volume of air which passes through thesystem in a proportionate amount.

Closing of all of the registers will eifect a substantial closure of thedamper d0, keeping, in the bonnet, the heat which is generated in thefurnace; and of course the furnace will be shut off by-the temperaturelimit switch, thus saving the fuel, which would otherwise be lost by thefurnace heating up in spite of the registers being closed.

The present system is thus adapted to regulate the amount of air passingthrough the system and out of the registers in proportion to the numberof registers that are open, and to diminishand the butterfly damperwhich it actuates are directly mounted on the same shaft, as may be donewhen this mechanism is installed in the partition of a standard winterair conditioning unit. In this case the partition is indicated by thenumeral 80, and it is provided with a laterally projecting housing 8|,similar to the housing 65, previously described, and communicating withthe space 82 on the hot air side of the partition 80. The vane 83operates similar to the vane 68, but it is fixedly mounted on the shaft85, which also supports the butterfly valve 85 located in the conduit 86that is adjacent to the conduit 8|. The hot air pipe 86 is again used todirect hot air from the top of the furnace bonnet on a thermostat 4|like that of Fig. 1, and all of the other details of the system may beexactly as described in Fig. 1.

The operation of the device of Fig. 3 is practically the same as that ofFig. 1, except that the vane 83 actuates the damper 85 directly throughthe shaft 84.

Referring now to Fig. 4, this is another diagrammatic illustration of amodification which is similar to Fig. 1, but instead of having the pipe,which conducts a sample of the hot air from the furnace casing,discharge on the bellows thermostat, this pipe may be located anywhereand may have a bulb containing the expansible fluid in it, the bulbbeing connected by a tube to the bellows. has a small pipe 89 whichcommunicates with the cold air inlet l8, and which is provided with thesame damper 11. The pipe 81 contains a bulb which communicates by meansof tube 9| with bellows 92. In some cases the bulb 90 might be locatedin the furnace bonnet ID.

The operation of this modified form of the heating system issubstantially the same as described with respect to Fig. 1.

I desire it to be understood that where thermoplastic bellows aredisclosed throughout the present application, other types ofthermostats, such as bimetallic thermostats or the wafer type ofthermostats may also be employed,

Referring now to Fig. 5, this is an additional improvement over theheating system disclosed in my prior Patent No. 2,275,429, Variablespeed pulley, which issued March 10, 1942. i

In this modification a thermostatically controlled variable diameterpulley is employed for effecting a zone control, as achieved by thesystem of Fig. l.

The thermostatically controlled pulley 22 includes a fixed pulleysection 28, upon which is slidably mounted a movable pulley section 29,both of these pulley sections having the opposed frusto-conical surfaces3|], 3| for engaging the V belt 2|. The pulley sections 28 and 29 arecontrolled by a thermostat 32, which may be of the bellows type, andwhich has its right or fixed end carried by a frame 33 or housing ofsubstantially U shape.

The legs 34, 35 arefixedly secured to the hub 36 of the fixed pulleysection 28. The movable pulley section 29 has a slot 31 for receivingthe legs of the frame so that this section may slide, but cannot rotaterelative to the fixed pulley section 28. I

The thermostat 32 reacts against the frame 33 and acts on the end of thehub 38 on the movable pulley section to urge'the two pulley sectionstogether.

Referring to Figs. 6 and '7, Fig. 6 shows the "pulley in its position ofmaximum diameter, the

thermostat havin expanded to force the two pulley sections together, thebelt riding outward on the frusto-conical surfaces 30 and 3| to theposition shown.

Fig. '7 shows the position of the parts when the thermostat iscontracted and the belt has forced the sections apart until it almostrides on the hub 38.

The bellows thermostat 32 is preferably filled with a suitable supply ofvolatile refrigerant, which begins to vaporize at a predeterminedtemperature and is sufficient in amount so that all is vaporized whenthe thermostat has expanded to the maximum pulley diameter.

Thus the thermostat will not be ruptured by additional expansion of therefrigerant, which takes place merely on superheating, and will not beexcessive. Various types of refrigerant may be used, as described in myprior application; but for an air conditioning installation I prefer touse trichloromonofiuoromethane (F11). The refrigerantselected woulddepend upon the range of temperatures desired.

The thermostat 32 of the variable diameter pulley 22 is preferablysubjected to the action of a. sample or specimen of air fromthe top ofthe In this embodiment the hot air pipe 88 furnace bonnet it, and thismay be accomplished by extending a small hot air conduit 39 from the topof the furnace bonnet down into the housing I! into a position where theaxially turned end of the conduit 39 surrounds the thermostat of thepulley 22.

Thus, when the blower is being driven, there will .be a circulation ofhot air from the furnace bonnet directly to the thermostat 32 so thatthe variable diameter pulley 22 is actuated responsive to thetemperature of the air which is being discharged from the furnacebonnet.

The operation of this part of the system so far may be substantially asdescribed in my prior Patent No. 2,275,429; the details of thethermostatic pulley may also be as described therein.

As the temperature of the air increases, the thermostat 32 expands,driving the pulley sections together and increasing the effectivediameter of the driving pulley 22. This increases the speed of rotationof the blower shaft l8 and increases the volume of air passing throughthe furnace bonnet l0.

As the temperature of the furnace increases, a greater volume of air maybe blown through it. As the temperature of the air discharged from thefurnace bonnet decreases, the blower is slowed down, and thus there areno cold drafts of air blown into the room when the present system isused, although the blower is driven by a constant speed motor.

In addition to this result, the present modification is adapted toeffect a zone control of the hot air which is discharged from thefurnace bonnet H). For this purpose the conduit 39, which extends fromthe top of the bonnet l and conducts air tothe thermostat 32, is againprovided with a damper 11 adapted to be actuated by a pressureresponsive vane 68 in a manner similar to that disclosed in Fig. 1. Allof the same interconnecting mechanism may be employed, as shown in Fig.1; or, when this device is installed in the partition of a standardwinter air conditioning unit, the vane may be connected to the damper,as shown in Figs. 2 and 3.

The operation of this modification is as follows: When a register isclosed, there is an increase of the static pressure in all of the hotair ducts, including the one in which the pressure responsive device islocated. It does not matter which register is closed, as the closure ofone of the registers introduces a restriction to the outlet of the hotair from the system so that there is necessarily an increase in .staticpressure in all of the hot air ducts.

This tends to move the vane 68 downward in Fig. 5 and tends to close thedamper 11. This diminishes the amount of hot air which is discharged onthe thermostat 32 of the variable diameter pulley and causes thethermostat to contract slightly; The contraction of the thermostatdiminishes the efiective diameter of the pulley, comprising the twosections 25, 26, so that the blower is driven more slowly.

The speed of the blower may thus be made proportional to the number orsize of registers which are closed, and the amount of air which isdriven through the system will thus be made responsive to the number ofregisters that are left open.

It will thus be observed that I have-invented an improved heating systemin which there is eflected an automatic zone control for regulating theamount of air that is driven through the system by the blower, inaccordance with the d iillmber of registers that may be open at any Myimproved heating system may be embodied in any of the modern existinginstallations by merely adding the devices which are necessary toefl'ect this control, while still utilizing the same blower and the sameconstant speed motor and other equipment of the heating system.

While I have illustrated a preferred embodiment of my invention, manmodifications may be made without departing from the spirit of theinvention, and I do not wish to be limited to the precise details ofconstruction set forth, but desire to avail myself of all changes withinthe scope of the appended claims.

Having thus described my invention, what I claim as new and desire .tosecure by Letters Patent of the United States, is:

1. In a heating system, the combination with a hot air furnace having afurnace housing for circulation of air to be heated by the furnace, saidhousing having a cold air inlet, a blower connected to said inlet, and asubstantially constant speed motor for driving said blower, said housingalso having a plurality of outlets and conduits leading to the variousrooms to be heated, each of said rooms being provided with adjustableregister openings and conduits of suitable proportion to the size of theroom, whereby at the full register opening and full air circulation bythe blower, each room receives a predetermined amount of heat, a damperlocated to throttle the supply of air by the blower to the furnacehousing, and a thermostat for controlling said damper, said thermostatbeing connected to' the damper in such manner that an increase intemperature of the thermostat, resulting in its expansion, tends to openthe damper, and contraction of the thermostat, due to lack of heat andreduced temperature of the thermostat, tends to close the damper, aconduit leading from a. point in the housing and conduit system, whichis filled with hot air, for conducting hot air to the space surroundingthe thermostat, and a pressure responsive flap pivotally mounted on oneof the hot air conduits of the system, and forming a movable wall whichmoves responsive to pressure of the hot air in the system, said flapbeing mechanically connected to a damper located in the latter conduitbetween the thermostat and the source of hot air, the said flap being soconnected to said latter damper that upon closing of a register in aroom, the increase in pressure near the hot air end of the system causesthe flap to move to effect a partial closure of said damper, saidpartial closure throttling the hot air, which influences the temperatureof the thermostat, and the relative cooling of the thermostat eifectinga partial closure of the damper throttling the cold air inlet, to reducethe total volume of air circulated through the system responsive to theclosure of a register, so that the hot air supplied will still be insuitable volume for the remaining registers.

2. In a heating system, the'ccmbination with a hot air furnace having afurnace housing for circulation of air to be heated by the furnace, saidhousing having a cold air inlet, a blower connected to said inlet, and asubstantially constant speed motor for driving said blower, said housingalso having a plurality of outlets and conduits leading to the variousrooms to be heated, each of said rooms being provided with adjustableregister openings and conduits of suitable proportion to the size of theroom, whereby at the full register opening and full air circulation 9 bythe blower, each room receives a predetermined amount of heat, a damperlocated to throttle the supply of air by the blower to the furnacehousing, and a thermostat for controlling said damper, said thermostatbeing connected to the damper in such manner that an increase intemperature of the thermostat, resulting in its expansion. tends to openthe damper, and contraction of the thermostat, due to lack of heat andreduced temperature of the thermostat, tends to. close the damper, aconduit leadin from a point in the housing and conduit system, which isfilled with hot air, for conducting hot air to the space surrounding thethermostat, and a pressure responsive flap pivotally mounted on one ofthe hot air conduits of the system, and forming a movable wall whichmoves responsive to pressure of the hot air in the system, said flapbeing mechanically connected to a damper located in the latter conduitbetween the thermostat and the source of hot air, the said flap being soconnected to said latter damper that upon closing of a register in aroom, the increase in pressure near the hot air end of the system causesthe flap to move to efi'ect .a partial closure of said damper, saidpartial closure throttling the hot air, which influences the temperatureof the thermostat, and the relative cooling of the thermostat effectinga partial closure of the damper, throttling the coldair inlet, to reducethe total volume of air circulated through the system responsive to theclosure of a register, so that the hot air supplied will still be insuitable Volume for the remaining registers, said flap being pivotallymounted in a fiat sided box attached to and in communication with a hotair conduit, and the weight of the said flap being counter-balanced byan oppositely extending arm carrying a balance weight.

3. In a heating system, the combination of a hot air furnace having ahousing and having a cold air inlet and a plurality of hot air outlets,a blower having its outlet connected to the cold air inlet, and having athrottling valve interposed between the blower and said inlet, asubstantially constant speed motor for driving said blower, a cold airinlet housing surrounding the blower and motor, a thermostat located insaid cold air inlet housing, a plurality of conduits leading from thehot air outlets of the furnace housing to various rooms. and closableregisters'at the ends of said conduits in said rooms, each room havingits conduit and register proportionate in opening .size to the size ofthe room, an auxiliary conduit leading from a point in the system havinga supply ofhot air under pressure, and extending to a point adjacentsaid thermostat to discharge hot air on the thermostat, said thermostatbein connected to the throttling valve in the cold air inlet in suchmanner as to close said valve when the thermostat is cold and to openthe valve as the thermostat becomes lceated in proportion to itstemperature, a throttling valve in said auxiliary conduit, a pressureresponsive device connected to be subjected to the pressure of the hotair in the upper part of the system. and mechanical connections betweensaid pressure responsive device and said latter throttling valve, toeffect a partia1 closure of said latter throttling valve wheneverpressure is increased in the system, the increase in pressure in theupper part of the hot air system closing said latter throttling valveand diminishing the supply of hot air to the vicinity of the thermostat,to reduce the temperature of the thermostat and proportionally to closethe throttling valve in the cold air inlet, to reduce the total volumeof 10 I air circulating in the system, to maintain a substantiallyconstant air pressure in the system.

4. In a heating system, the combination of a hot air furnace having ahousing and having a cold air inlet and a plurality of hot air outlets,a blower having its outlet connected to the cold air inlet, and having athrottling .valve interposed between the blower and said inlet, asubstantially constant speed motor for driving said blower, a cold airinlet housing surrounding the blower and motor, a thermostat located insaid cold air inlet housing, a plurality of conduits leading from thehot air outlets of the furnace housing to various rooms, and closableregisters at the ends of said conduits in said rooms, each room havingits conduit and register proportionate in opening size to the size ofthe room, an auxiliary conduit leading from a point in the system havinga supply of hot air under pressure, and extending to a point adjacentsaid thermostat to discharge hot air on the thermostat, said thermostatbeing connected to the throttling valve in the cold air inlet in suchmanner as to close said valve when the thermostat is cold and to openthe valve as the thermostat becomes heated in proportion to itstemperature, a throttling valve insaid auxiliary conduit, a pressureresponsive device connected to be subjected to the pressure of the hotair in the upper part of the system, and mechanical connections betweensaid pressure responsive device and said latter throttling valve, toeffect a partial closure of said latter throttling valve wheneverpressure is increased in the system, the increase in pressure in theupper part of the hot air system closing said latter throttling valveand diminishing thesupply of hot air to the vicinity of the thermostat,to reduce the temperature of the thermostat and proportionally to closethe throttling valve in the cold air inlet, to reduce the total volumeof air circulating in the system, to maintain a substantially constantair pressure in the system, the said pressure responsive devicecomprising a pivoted wall flapopen to atmosphere at one side andsubjected tothe hot air under pressure on the other side, said wall flaphaving its weight counter-balanced by an oppositely extending arm with acounter-weight.

5. In a heating system, the combination of a hot air furnace having ahousing and having'a.

cold air inlet and a plurality of hot air outlets, a blower having itsoutlet connected to the cold air inlet, and having a throttling valveinterposed between the blower and said inlet, a substantially constantspeed motor for driving said blower, a cold air inlet housingsurrounding the blower and motor, a thermostat located in said cold airinlet housing, a plurality of conduits leadingfrom the hot air outletsof the furnace housing to various rooms, and closable registers at theends of said conduits in said rooms, each room having its conduit andregister proportionate in opening size to the size of the room, anauxiliary conduit leading from a point in the system having a supply ofhot air under pressure, and extending to a point adjacent saidthermostat to discharge hot air on the thermostat, said thermostat beingconnected to the throttling valve in the 'cold air inlet in such manneras to close said valve when the thermostat is cold and to open the valveas the thermostat becomes heated in proportion to its temperature, athrottling valve in said auxiliary conduit, a pressure responsive deviceconnected to be subjected the pressure of the hot air in the upperpartof the system, and mechanical connections between said pressureresponsive device 1 and said latter throttling valve, to effect apartial closure of said latter throttling valve whenever pressure isincreased in.the system, the increase in pressure in the upper part ofthe hot air system closing said latter throttling valve and diminishingthe supply of hot air to the vicinity of the thermostat, to reduce thetemperature of the thermostat and proportionally to close the throttlingvalve in the cold air inlet, to reduce the total volume of aircirculating in the system, to maintain a substantially constant airpressure in the system, said system operating responsive to the closureof one or more registers, said closure reducing the outlet area and thusincreasing the air pressure in the hot air pipes of the system andmoving said flap to reduce the hot air supplied to the thermostat, whichin turn closes the throttling valve in the cold air inlet.

WIILIAM W. HALHNAN.

REFERENQES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

